TVLine has learned that the familiar face from such shows as Once Upon a Time, Mad Men and Lost will guest-star as Frederick, the brother of Paget Brewster’s Sara (aka John Stamos’ on-screen baby mama).

Grandfathered, in which Stamos’ rakish restaurateur Jimmy discovers he has a 1) son and 2) granddaughter, premieres Tuesday, Sept. 29 at 8/7c, where it leads into fellow freshman The Grinder (starring the similarly ageless Rob Lowe).